Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $226.32   8.555%   $245.6817   $245.68   $245.70   $245.70  
  Purchase #2 $204.64   4.296%   $213.4313   $213.43   $213.45   $213.40  
  Purchase #3 $74.39   8.325%   $80.583   $80.58   $80.60   $80.60  
  Purchase #4 $32.56   8.872%   $35.4487   $35.45   $35.45   $35.40  
  Purchase #5 $178.56   3.632%   $185.0453   $185.05   $185.05   $185.00  
  Purchase #6 $187.97   12.147%   $210.8027   $210.80   $210.80   $210.80  
  Purchase #7 $236.49   10.107%   $260.392   $260.39   $260.40   $260.40  
  7 purchase totals = $1,140.93       $1,231.3847   $1,231.38   $1,231.45   $1,231.30